Wireless communication devices or units such as receivers and transceivers supporting high and ultra high bandwidth and data rates in corresponding systems are being developed. As these systems have evolved higher frequency channels with larger bandwidths and more sophisticated encoding and modulation schemes are being employed. For example, IEEE 802.15 working group is developing standards for short range communications that specify channels from 3.1 GHz to 5.15 GHz and from 5.825 GHz to 10.6 GHz and data rates as high as 1.35 Gbps (billion bits per second). These systems with wideband or ultra wideband channels that are often referred to as complex channels, present various problems for practitioners. One problem is inter-symbol interference (ISI) that is normally dominated by multipath effects, e.g. the impact of receiving multiple signals or rays as a result of various combinations of reflections of a transmitted signal before it arrives at the receiver location.
It is known to use equalizers and corresponding methods to improve or reduce the degree of ISI. Generally a training period is used where a known signal is transmitted. When the receiver recovers the known signal various techniques can be used to compensate or restore the recovered signal to a reasonable approximation of the known signal. The resulting compensation or equalization information or parameters can then be used to compensate subsequently and unknown signals that are received. While various techniques exist for performing equalization they suffer from various problems, such as excessive computational complexity or latency or failure to address the relevant vagaries of a complex channel. These shortcomings can be especially troublesome in cost and battery life constrained receivers with limited processing or computational resources.
One way to provide such equalization is by a combination of feedback and feed-forward signals. In such an equalizer system the processing speed of a feed-forward path is generally not critical. Although it is desirable to perform feed-forward within one symbol period, it is possible to accommodate a longer feed-forward processing time. However, feedback structures are typically much more sensitive to processing time, and must be accomplished within a single symbol period.
Thus a need exists for feedback/feed-forward equalizer designs that can complete the feed-forward and feedback processes within single symbol period without requiring too much circuit complexity.